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作者：xcheng_链接：https://www.jianshu.com/p/07fe489a53f2声明：本文已获
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http请求一直是开发中无法避免的存在，生命周期的管理也一直是开发者的痛点，稍不注意就在回调是抛出异常，如NullPointerException,showDialog导致的WindowLeaked等。
Google 最新推荐的 Lifecycle 架构就是可以让你自己的类拥有像 activity 或 fragment 一样生命周期的功能。
于是我决定采用lifecycle结合retrofit 将http请求和Activity或Fragment的生命周期相结合
本文将从以下几个方面一步步实现功能
多线程分发Lifecycle. Event
retrofit如何与其关联?自定义 CallAdapter.Factory
异步请求如何关联
同步请求如何关联
如果有不熟悉lifecycle的可以自行学习，这里不做介绍了
lifecycle官方文档地址：
https://developer.android.com/topic/libraries/architecture/lifecycle
activity 和fragment 是有声明周期的，有时候，我们的很多操作需要写在声明周期的方法中，比如，下载，文件操作等，这样很多情况下回导致，我们在activity中的声明周期方法中写越来越多的代码，activity或者fragment 越来越臃肿，代码维护越来越困难。使用lifecycle就可以很好的解决这类问题。
对于event的分发我们采用观察者模式，需要支持多线程环境，因为http请求可能在任意线程中发起。
首先定义一个 LifecycleProvider类,如下
/**
* 统一分发Activity和 Fragment的生命周期时间.
*/
public interface LifecycleProvider {
/**
* Adds an observer to the list. The observer cannot be null and it must not already
* be registered.
*
* @param observer the observer to register
* @throws IllegalArgumentException the observer is null
*/
void observe(Observer observer);
/**
* Removes a previously registered observer. The observer must not be null and it
* must already have been registered.
*
* @param observer the observer to unregister
* @throws IllegalArgumentException the observer is null
*/
void removeObserver(Observer observer);
/**
* A simple callback that can receive from {@link android.arch.lifecycle.Lifecycle}
*/
interface Observer {
/**
* Called when the event is changed.
*
* @param event The new event
*/
void onChanged(@NonNull Lifecycle.Event event);
}
}
实现类 为AndroidLifecycle 继承了LifecycleObserver接口监听Lifecycle event
public final class AndroidLifecycle implements LifecycleProvider, LifecycleObserver {
private final Object mLock = new Object();
@GuardedBy("mLock")
private final ArrayList<Observer> mObservers = new ArrayList<>();
/**
* 缓存当前的Event事件
*/
@GuardedBy("mLock")
@Nullable
private Lifecycle.Event mEvent;
@MainThread
public static LifecycleProvider createLifecycleProvider(LifecycleOwner owner) {
return new AndroidLifecycle(owner);
}
private AndroidLifecycle(LifecycleOwner owner) {
owner.getLifecycle().addObserver(this);
}
@OnLifecycleEvent(Lifecycle.Event.ON_ANY)
void onEvent(LifecycleOwner owner, Lifecycle.Event event) {
synchronized (mLock) {
//保证线程的可见性
mEvent = event;
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onChanged(event);
}
}
if (event == Lifecycle.Event.ON_DESTROY) {
owner.getLifecycle().removeObserver(this);
}
}
@Override
public void observe(Observer observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized (mLock) {
if (mObservers.contains(observer)) {
return;
}
mObservers.add(observer);
if (mEvent != null) {
observer.onChanged(mEvent);
}
}
}
@Override
public void removeObserver(Observer observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized (mLock) {
int index = mObservers.indexOf(observer);
if (index == -1) {
return;
}
mObservers.remove(index);
}
}
}
使用时只要在onChanged方法中就可以处理对应的事件,使用如下
LifecycleProvider provider = AndroidLifecycle.createLifecycleProvider(this);
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
provider.observe(new LifecycleProvider.Observer() {
@Override
public void onChanged(@NonNull Lifecycle.Event event) {
//do...
}
});
}
observe方法不依赖于主线程，可以在任何地方调用。这样二次分发设计的目的有两个
owner.getLifecycle().addObserver(LifecycleObserver)方法是线程不安全的，需要依赖主线程
可以缓存最新的Lifecycle.Event
retrofit 如何才能关联生命周期呢，通用的做法肯定是自定义CallAdapter.Factory，我们可以返回我们想要的自定义Call，在Call接口添加bindToLifecycle方法于LifecycleProvider相关联
自定义Call接口如下，添加了绑定生命周期的方法，这里只展示核心方法
public interface Call<T> extends Callable<T>, Cloneable {
//忽略其他代码
/**
* 绑定生命周期
*
* @param provider LifecycleProvider
* @param event {@link Lifecycle.Event}, {@link Lifecycle.Event#ON_ANY} is not allowed
* @return LifeCall
*/
LifeCall<T> bindToLifecycle(LifecycleProvider provider, Lifecycle.Event event);
/**
* default event is {@link Lifecycle.Event#ON_DESTROY}
*
* @param provider LifecycleProvider
* @return LifeCall
* @see Call#bindToLifecycle(LifecycleProvider, Lifecycle.Event)
*/
LifeCall<T> bindUntilDestroy(LifecycleProvider provider);
}
且看如何实现此接口 RealCall
final class RealCall<T> implements Call<T> {
//忽略其他代码
@Override
public LifeCall<T> bindToLifecycle(LifecycleProvider provider, Lifecycle.Event event) {
Utils.checkNotNull(provider, "provider==null");
Utils.checkNotNull(event, "event==null");
if (event == Lifecycle.Event.ON_ANY) {
throw new IllegalArgumentException("ON_ANY event is not allowed.");
}
return new RealLifeCall<>(clone(), event, provider);
}
@Override
public LifeCall<T> bindUntilDestroy(LifecycleProvider provider) {
return bindToLifecycle(provider, Lifecycle.Event.ON_DESTROY);
}
}
LifeCall 生命周期管理的接口类,它继承了LifecycleProvider.Observer,因此可以在onChanged方法接收分发的Lifecycle.Event
public interface LifeCall<T> extends Callable<T>, LifecycleProvider.Observer {
/**
* Returns true if this call has been disposed.
*
* @return true if this call has been disposed
*/
boolean isDisposed();
/**
* The method may be called concurrently from multiple
* threads; the method must be thread safe. Calling this method multiple
* times has no effect.
* <p>
* like {@code Observable#doOnDispose(Action)},{@code SingleSubject#onSuccess(Object)}
* <p>
* you can invoke with {@link Lifecycle.Event#ON_ANY} to dispose from outside immediately.
*/
@Override
void onChanged(@NonNull Lifecycle.Event event);
}
且看如何实现此接口RealLifeCall
在onChanged中判断，当event参数为指定的event时取消请求，并且标记为disposed，从provider中移除RealLifeCall观察对象。注意的是可以手动调用LifeCall.onChanged(LifeCycle.Event.ON_ANY)取消请求用于你想处理的任何场景，如果isDisposed()返回为true，在异步Callback调用的情况下是不会回调的。
final class RealLifeCall<T> implements LifeCall<T> {
private final Call<T> delegate;
private final Lifecycle.Event event;
private final LifecycleProvider provider;
private final AtomicBoolean once = new AtomicBoolean();
RealLifeCall(Call<T> delegate, Lifecycle.Event event, LifecycleProvider provider) {
this.delegate = delegate;
this.event = event;
this.provider = provider;
provider.observe(this);
}
//忽略其他代码
@Override
public void onChanged(@NonNull Lifecycle.Event event) {
if (this.event == event
|| event == Lifecycle.Event.ON_DESTROY
//Activity和Fragment的生命周期是不会传入 {@code Lifecycle.Event.ON_ANY},
//可以手动调用此方法传入 {@code Lifecycle.Event.ON_ANY},用于区分是否为手动调用
|| event == Lifecycle.Event.ON_ANY) {
if (once.compareAndSet(false, true)/*保证原子性*/) {
delegate.cancel();
provider.removeObserver(this);
}
}
}
@Override
public boolean isDisposed() {
return once.get();
}
}
如何返回Call ?自定义CallAdapter.Factory
retrofit的解耦灵活我们可以做很多自定义的配置，自定义Factory返回我们的Call接口对象，只需在创建retrofit对象是调用addCallAdapterFactory(CallAdapterFactory.INSTANCE)添加进去即可。
注：executor默认为Android主线程调度使用，Callback回调函数会在对应线程执行。详情可以看retrofit2.Platform.Android.defaultCallbackExecutor()方法
public final class CallAdapterFactory extends CallAdapter.Factory {
private static final String RETURN_TYPE = Call.class.getSimpleName();
public static final CallAdapter.Factory INSTANCE = new CallAdapterFactory();
private static final Executor OPTIONAL_NULL_EXECUTOR = new Executor() {
@Override
public void execute(@NonNull Runnable command) {
command.run();
}
};
private CallAdapterFactory() {
}
@Override
public CallAdapter<?, ?> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
if (getRawType(returnType) != Call.class) {
return null;
}
if (!(returnType instanceof ParameterizedType)) {
throw new IllegalArgumentException(
String.format("%s return type must be parameterized as %s<Foo> or %s<? extends Foo>", RETURN_TYPE, RETURN_TYPE, RETURN_TYPE));
}
final Type responseType = getParameterUpperBound(0, (ParameterizedType) returnType);
final Executor executor = Utils.isAnnotationPresent(annotations, SkipCallbackExecutor.class)
? null
: retrofit.callbackExecutor();
return new CallAdapter<Object, Call<?>>() {
@Override
public Type responseType() {
return responseType;
}
@Override
public Call<Object> adapt(retrofit2.Call<Object> call) {
if (executor != null) {
return new RealCall<>(executor, call);
}
return new RealCall<>(OPTIONAL_NULL_EXECUTOR, call);
}
};
}
}
丰富的Callback接口
支持开始、结束、成功、失败、异常统一解析、简单的数据二次处理操作，HttpError统一包装异常信息
public interface Callback<T> {
/**
* @param call The {@code Call} that was started
*/
void onStart(Call<T> call);
@NonNull
HttpError parseThrowable(Call<T> call, Throwable t);
/**
* 过滤一次数据,如剔除List中的null等,默认可以返回t
*/
@NonNull
T transform(Call<T> call, T t);
void onError(Call<T> call, HttpError error);
void onSuccess(Call<T> call, T t);
/**
* @param t 请求失败的错误信息
*/
void onCompleted(Call<T> call, @Nullable Throwable t);
}
异步调用
定义接口
@FormUrlEncoded
@POST("user/login")
Call<LoginInfo> getLogin(@Field("username") String username, @Field("password") String password);
安全的异步发起请求：
public class MainActivity extends AppCompatActivity {
LifecycleProvider provider = AndroidLifecycle.createLifecycleProvider(this);
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
RetrofitFactory.create(ApiService.class)
.getLogin("loginName", "password")
//.bindUntilDestroy(provider)
.bindToLifecycle(provider, Lifecycle.Event.ON_STOP)
.enqueue(new DefaultCallback<LoginInfo>() {
@Override
public void onStart(Call<LoginInfo> call) {
showLoading();
}
@Override
public void onError(Call<LoginInfo> call, HttpError error) {
Toast.makeText(MainActivity.this, error.msg, Toast.LENGTH_SHORT).show();
}
@Override
public void onSuccess(Call<LoginInfo> call, LoginInfo loginInfo) {
Toast.makeText(MainActivity.this, "登录成功", Toast.LENGTH_SHORT).show();
}
@Override
public void onCompleted(Call<LoginInfo> call, @Nullable Throwable t){
hideLoading();
}
});
}
}
如何同步调用
一般同步调用的场景不多，一些连续且相互依赖的请求可以使用同步请求减少逻辑复杂性
如：注册成功后直接登录，如果采用异步的方式实现，回调接口缠绕在一起，代码不好维护。采用同步的方式实现更为方便。
@FormUrlEncoded
@POST("user/register")
Call<RegisterInfo> register(@Field("username") String username, @Field("password") String password);
@FormUrlEncoded
@POST("user/login")
Call<LoginInfo> getLogin(@Field("username") String username, @Field("password") String password);
new Thread(){
@Override
public void run() {
super.run();
try {
RegisterInfo registerInfo=RetrofitFactory.create(ApiService.class)
.register("loginName", "password")
.bindToLifecycle(provider, Lifecycle.Event.ON_STOP)
.execute();
//注册成功开始登录
LoginInfo loginInfo=RetrofitFactory.create(ApiService.class)
.getLogin("loginName", "password")
.bindToLifecycle(provider, Lifecycle.Event.ON_STOP)
.execute();
//登录成功
} catch (Throwable throwable) {
//异常处理
throwable.printStackTrace();
}
}
}.start();
这里涉及二个问题
关于Thread，可以自行用线程池实现，这里制作演示
线程调度，成功和失败的结果需要回调到主线程中，android中回调主线程采用的Handler.post(Runnable)或者postDelayed(Runnable, long)方法实现，当主线程调度执行run方法是可能Activity或者Fragment已经被销毁。那么怎样才能安全的回调到主线程呢？
调度方法和生命周期关联，在主线程执行时再次做判断。NetTaskExecutor 是做的Handler的封装
public final class ToMainThread implements LifecycleProvider.Observer {
@Nullable
private volatile Lifecycle.Event mEvent;
private final LifecycleProvider provider;
public ToMainThread(LifecycleProvider provider) {
this.provider = provider;
provider.observe(this);
}
public void to(@NonNull final Runnable runnable, final Lifecycle.Event event) {
NetTaskExecutor.getInstance().postToMainThread(new Runnable() {
@Override
public void run() {
if (mEvent == event || mEvent == Lifecycle.Event.ON_DESTROY)
return;
runnable.run();
}
});
}
public void toDelayed(@NonNull final Runnable runnable, final Lifecycle.Event event, long delayMillis) {
NetTaskExecutor.getInstance().postToMainThreadDelayed(new Runnable() {
@Override
public void run() {
if (mEvent == event || mEvent == Lifecycle.Event.ON_DESTROY)
return;
runnable.run();
}
}, delayMillis);
}
@Override
public void onChanged(@NonNull Lifecycle.Event event) {
this.mEvent = event;
if (event == Lifecycle.Event.ON_DESTROY) {
provider.removeObserver(this);
}
}
}
完整的同步执行代码如下，这样处理完全关联了生命周期。不会出任何问题
结束
github 地址：https://github.com/xchengDroid/retrofit-helper
欢迎提出疑问和建议。
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